One of the most common complaints of hearing aid users is that their own voice sounds unnatural: boomy, hollow or echoing. Poor sound quality of a person's own voice is also one of the top ten reasons why some hearing aids end up in the drawer. This problem with a person's own voice is very often due to the so-called occlusion effect which occurs because the body-conducted contribution to a person's perception of his/her own voice is trapped in the cavity between the occluding earmold of the hearing instrument and the tympanic membrane. The result is a build-up of sound pressure at low frequencies that may be as much as 30 dB relative to the open-ear. Typically, the occlusion effect has a flat maximum between 80-500 Hz and vanishes above 1 kHz. In the open-ear condition and at the low frequencies considered here, the body-conducted contribution is insignificant compared to the air-conducted contribution. In today's hearing aid dispensing there are basically three ways to address the client's eventual occlusion problem with his/her own voice. First, the earmold (or ITE hearing aid) may be equipped with a vent through which the body-conducted part of his/her own voice can dissipate. Secondly, it has been shown that CIC instruments that are fitted with a seal in the bony part of the ear canal can solve or at least reduce the occlusion problem in many cases. Unfortunately, bony sealed CICs have earned a bad reputation for introducing physical discomfort and are hence rarely dispensed. Thirdly, occlusion problems may be dealt with by counseling—along the lines of “You'll get used to it!”. A number of hearing aid users do not manage to get used to it, and they prefer to live with their hearing disorder un-aided.
In U.S. Pat. No. 4,985,925 an active noise reduction based on a negative feed back electro-acoustical system is shown. The system consists of an electronic earplug seated in the concha fossa combining active and passive noise reduction in the quiet zone at the ear, a bilateral transducer circuit which drives a speaker as an acoustical velocity source, a shunt feed back control filter network which improves stability and increases noise reduction, and a combined input noise-filter/feed back system. A typical application is in a noisy environment for hearing protection and for improved communication capability.